1. Field of the Invention
The present invention relates generally to an internal combustion engine and more specifically to a method of calibrating a pressure sensor used therein.
2. Description of the Prior Art
Various attempts have been made to control the combustion process occuring within a combustion chamber of an internal combustion engine via sensing the pressure produced therein and effecting various measures in response thereto. One example of such is found in Japanese Provisional Patent Publication No. Sho 49-17973 wherein an ionization current is produced in accordance with combustion chamber pressure and the ignition timing of the of the engine varied to produce the maximum possible pressure. Another example is found in Japanese Provisional Patent Publication No. Sho 49-29209 wherein both the pressure in the combustion chamber and the crankangle are simultaneously sensed and the angle at which the maximum pressure occurs compared with a standard angle for the purposes of determining an optimal angle at which to effect ignition.
Further examples are found in:
Japanese Provisional Patent Publication No. Sho 53-56429 in which the disclosed arrangement seeks to control the ignition timing so that the peak pressure in the combustion chamber does not exceed a level whereat noxious (exhaust gas) components are generated in undesirable quantities.
Japanese Provisional Patent Publication No. Sho 57-77935 discloses an arrangement wherein the difference between the sensed maximum combustion chamber pressure and a standard are compared to control the maximum pressure in accordance with a predetermined standard or schedule.
Japanese Provisional Patent Publication No. Sho 52-151432 in which the disclosed arrangement utilizes the fact that ratio of the maximum pressure (Pmax) and a motoring pressure (Pm) increases with ignition timing advance to a maximum value which is essentially equal to the MBT (minimum spark advance for best torque) and whichis essentially independent of operational parameters such as engine speed, induction vacuum, air-fuel ratio and the like. This system is meritorious in that it is uncessary to effect compensations for changes in atmospheric conditions (e.g. atmos. pressure), engine characteristics and the like as compared with systems wherein generally average ignition timings are programmed in accordance with test results.
Japanese Provisional Patent Publication No. Sho 53-60431 teaches a system wherein ignition timing is advanced until knocking occurs and wherein the maximum combustion chamber pressure: motoring pressure ratio is controlled to a predetermined value in a manner similar to that disclosed in connection with Japanese Provisional Patent Publication No. Sho 52-151432.
Japanese Provisional Patent Publication No. Sho 52-39038 teaches an arrangement wherein control is effected to operated the engine at a minimum fuel consumption rate by varying the spark timing, sensing the torque variation and discrimiating between the phases of torque and ignition phase variations and controlling the ignition timing in response thereto.
However, a problem common to all of the above previously proposed arrangements comes in that the effect of the motoring pressure (viz., the pressure produced by only the movement of the piston) is not discriminated from the pressure actually produced by the combustion of the air-fuel mixture. Accordingly, it is impossible to distinguish whether the pressure produced by combustion has decreased (for example) or the combustion process per se changed. Accordingly, it has been impossible until this time to accurately determine the nature of the combustion process and therefore impossible to appropriately control the ignition timing and/or other operational parameters such as air-fuel ratio and the like to an optimal level.